RearEnd Upgrade
01-10-2015, 09:09 PM
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RearEnd Upgrade
hey everyone, i currently have an 87 GTA. I finished rebuilding the motor last weekend and I am hoping to get it to the paint shop this week. Either way, with this L98/700r4 combo I want 
<--- dual skids 
Any suggestions on upgrading my stock rearend or is there a cheaper swap with a quicker final drive setup? Open to anything although my wallet isn't 
<--- dual skids Any suggestions on upgrading my stock rearend or is there a cheaper swap with a quicker final drive setup? Open to anything although my wallet isn't 
01-10-2015, 10:06 PM
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01-11-2015, 12:27 AM
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Re: RearEnd Upgrade
I'm guessing with an 87 and L98/700R4, there's a good chance you have a 3.27 geared 9 bolt.
Best suggestion is to run what you have until it breaks but until then, start saving up for a 9", or 12 bolt as there is no cheap and easy upgrade.
With a good 383 and a TH350 trans, I pushed a 3.27 9 bolt into the 11's before swapping it out for something that allowed me to get a deeper gear. A 10 bolt with 4.10 gear allowed be into the low 11's and I finally installed a 9" to survive behind a transbrake.
Best suggestion is to run what you have until it breaks but until then, start saving up for a 9", or 12 bolt as there is no cheap and easy upgrade.
With a good 383 and a TH350 trans, I pushed a 3.27 9 bolt into the 11's before swapping it out for something that allowed me to get a deeper gear. A 10 bolt with 4.10 gear allowed be into the low 11's and I finally installed a 9" to survive behind a transbrake.
01-11-2015, 10:28 AM
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Re: RearEnd Upgrade
Only drag racing for this one will be to the grocery store lol this is my daily. Please dont bash me but did all GTAs come with the L98? when i got the car the man said it had the TPI305 and this currently was the L98 vette motor (which it is) They had rebuilt the bottom end and put a Voodoo .504/.525 cam in it but in a hurry to finish they put some old pick-n-pull heads on it, kept the 305 setup. I bought some brand new ported 2.02 heads with .550 springs and screw-in studs, new injectors, new rods, new rockers, TB airfoil, as well as a EGR and 9th injector delete. I haven't got my Memcal re-programmed yet. Trans is supposedly rebuilt with kit (shifts hard but pretty smooth) I am just debating if it is a true GTA or just a Trans with the emblems/rims/taillights etc.
01-11-2015, 10:30 AM
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Re: RearEnd Upgrade
I'm guessing with an 87 and L98/700R4, there's a good chance you have a 3.27 geared 9 bolt.
Best suggestion is to run what you have until it breaks but until then, start saving up for a 9", or 12 bolt as there is no cheap and easy upgrade.
With a good 383 and a TH350 trans, I pushed a 3.27 9 bolt into the 11's before swapping it out for something that allowed me to get a deeper gear. A 10 bolt with 4.10 gear allowed be into the low 11's and I finally installed a 9" to survive behind a transbrake.
Best suggestion is to run what you have until it breaks but until then, start saving up for a 9", or 12 bolt as there is no cheap and easy upgrade.
With a good 383 and a TH350 trans, I pushed a 3.27 9 bolt into the 11's before swapping it out for something that allowed me to get a deeper gear. A 10 bolt with 4.10 gear allowed be into the low 11's and I finally installed a 9" to survive behind a transbrake.
I just checked and it is the 10bolt 7.5. What is the ratio on these? Should I just run it until it breaks? Trending Topics
01-11-2015, 10:30 AM
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01-11-2015, 10:42 AM
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Re: RearEnd Upgrade
Found this comment on a different thread. Is there any truth or justice to this?? "Why not find out for yourself? Every V6 thirdgen in any yard will probably have 3.42s. Open but its still 3.42s. Its one of those upgrades where you wonder why you never did it sooner."
01-11-2015, 11:10 AM
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Re: RearEnd Upgrade
did all GTAs come with the L98?
vette motor (which it is)
they put some old pick-n-pull heads on it
Same thing goes for 350s in general. I cannot begin to count the number of times we see on this forum "PO told me it has a 350", "looks just like a 350", "runs too good to be a 305", "I heard {fill in the blank}s all came with 350s", and so on. Only way to know for sure is by the block casting number (NOT the stamping code) which is [sarcasm] conveniently located in a conspicuous and easily accessed place [/sarcasm], namely the top of the bell housing flange right behind the driver's side head. I'd STRONGLY urge you to get that casting number to verify what you've REALLY got before trying to mod it.
if it is a true GTA
10bolt 7.5. What is the ratio on these?
While you're changing the fluid, as you mentioned you are about to do (being the common-sensical new owner of a car that you are, you are doing what any such person would do as part of catching up on unknown deferred maintenance by replacing all the fluids), whatever you see in there, is what it is.
Is there any truth or justice to this??
01-11-2015, 11:32 AM
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Re: RearEnd Upgrade
No. 5-speed ones came with 305s for sure.
EVERY small block Chevy in EVERY used car is ALWAYS a "vette motor". That's one of the first things any beginning hot-rodder knows. The fantasy comes crashing down when one realizes that there are now about 25 times as many "vette motors" in the world as there have ever been Vettes. However in this case, THE ONLY thing that makes a Vette L98 a Vette L98, is its heads; so whatever "Vette"ness it once had, is now gone.
Another thing you'll learn as you gain experience in this hobby is, that metal parts have ABSOLUTELY NO MEMORY WHATSOEVER of the sheet metal (or fiberglass) that they have been wrapped in at any given stage of their life. No matter what body the parts have ever been in for however long, no sublime magic wafts itself out of the body and imbues the castings with any superior attributes. A rebuilt 350 short block that was in a Vette for some portion of its life is indistinguishable in every manner way shape form and fashion from a rebuilt 350 short block that has been exposed to any other body. So, in the interest of not advertising your n00bity, I would counsel you to leave all the "Vette" crap behind, as it just shows that you are gullible and inexperienced with stars in your eyes over something that sounds cool but you have no clue what it even means.
Same thing goes for 350s in general. I cannot begin to count the number of times we see on this forum "PO told me it has a 350", "looks just like a 350", "runs too good to be a 305", "I heard {fill in the blank}s all came with 350s", and so on. Only way to know for sure is by the block casting number (NOT the stamping code) which is [sarcasm] conveniently located in a conspicuous and easily accessed place [/sarcasm], namely the top of the bell housing flange right behind the driver's side head. I'd STRONGLY urge you to get that casting number to verify what you've REALLY got before trying to mod it.
Look at your SPID sheet. The RPO code for the GTA appearance package is Y84 if memory serves. (some one of you Firebird people please correct me if I've got it wrong, I'm sure you will anyway without me asking for it) If it has that, it's a GTA; if not, it's not. Pretty straightforward.
2.29, 2.41, 2.73, 2.92, 3.08, 3.23, 3.42, 3.73, or 4.10.
While you're changing the fluid, as you mentioned you are about to do (being the common-sensical new owner of a car that you are, you are doing what any such person would do as part of catching up on unknown deferred maintenance by replacing all the fluids), whatever you see in there, is what it is.
Yes and no. Depends on year and transmission. 6-cyl 5-spd cars in the later years generally do have that gear, similar auto cars usually have 3.23. 90-92 will have the better axles (larger diameter) with 28 splines instead of the earlier 26. Unfortunately however about 99.999% of all 6-cyl cars came with drum brakes, which in those same years, disc brake rears would have the good PBR setup instead of the crappy Saginaw setup they used up through 88. And a similar proportion come with an open (non-posi) carrier. So I'd suggest, if you find that the gears aren't to your liking, that since the gear set is one of the cheeeeeeepest parts of a rear, that you not worry about trying to score the ratio you want in the junkyard, but instead, find a 90-92 core with disc brakes, and put a good posi and whatever gears you want in it, rather than the other way around.
EVERY small block Chevy in EVERY used car is ALWAYS a "vette motor". That's one of the first things any beginning hot-rodder knows. The fantasy comes crashing down when one realizes that there are now about 25 times as many "vette motors" in the world as there have ever been Vettes. However in this case, THE ONLY thing that makes a Vette L98 a Vette L98, is its heads; so whatever "Vette"ness it once had, is now gone.
Another thing you'll learn as you gain experience in this hobby is, that metal parts have ABSOLUTELY NO MEMORY WHATSOEVER of the sheet metal (or fiberglass) that they have been wrapped in at any given stage of their life. No matter what body the parts have ever been in for however long, no sublime magic wafts itself out of the body and imbues the castings with any superior attributes. A rebuilt 350 short block that was in a Vette for some portion of its life is indistinguishable in every manner way shape form and fashion from a rebuilt 350 short block that has been exposed to any other body. So, in the interest of not advertising your n00bity, I would counsel you to leave all the "Vette" crap behind, as it just shows that you are gullible and inexperienced with stars in your eyes over something that sounds cool but you have no clue what it even means.
Same thing goes for 350s in general. I cannot begin to count the number of times we see on this forum "PO told me it has a 350", "looks just like a 350", "runs too good to be a 305", "I heard {fill in the blank}s all came with 350s", and so on. Only way to know for sure is by the block casting number (NOT the stamping code) which is [sarcasm] conveniently located in a conspicuous and easily accessed place [/sarcasm], namely the top of the bell housing flange right behind the driver's side head. I'd STRONGLY urge you to get that casting number to verify what you've REALLY got before trying to mod it.
Look at your SPID sheet. The RPO code for the GTA appearance package is Y84 if memory serves. (some one of you Firebird people please correct me if I've got it wrong, I'm sure you will anyway without me asking for it) If it has that, it's a GTA; if not, it's not. Pretty straightforward.
2.29, 2.41, 2.73, 2.92, 3.08, 3.23, 3.42, 3.73, or 4.10.
While you're changing the fluid, as you mentioned you are about to do (being the common-sensical new owner of a car that you are, you are doing what any such person would do as part of catching up on unknown deferred maintenance by replacing all the fluids), whatever you see in there, is what it is.
Yes and no. Depends on year and transmission. 6-cyl 5-spd cars in the later years generally do have that gear, similar auto cars usually have 3.23. 90-92 will have the better axles (larger diameter) with 28 splines instead of the earlier 26. Unfortunately however about 99.999% of all 6-cyl cars came with drum brakes, which in those same years, disc brake rears would have the good PBR setup instead of the crappy Saginaw setup they used up through 88. And a similar proportion come with an open (non-posi) carrier. So I'd suggest, if you find that the gears aren't to your liking, that since the gear set is one of the cheeeeeeepest parts of a rear, that you not worry about trying to score the ratio you want in the junkyard, but instead, find a 90-92 core with disc brakes, and put a good posi and whatever gears you want in it, rather than the other way around.
The first thing I did after tearing it down was run the number and it holds true to the accusations. The reason for the "pick-n-pull" head reference was that although they may not KNOW it (kz inanimate objects dont have a consciousness) regardless they were some worn out small valve heads with a spring rate not equivalent to what they had put in the motor
Thanks, I will check the code today to see if it is a true GTA and when i change fluids I will check the ratio manually to be sure.
Alright, thanks for clearing that up, it makes alot more sense to do the rearend that way.
Last edited by nikk2themax; 01-11-2015 at 12:03 PM.
01-11-2015, 01:07 PM
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Re: RearEnd Upgrade
There are many ways to go with the 7.5 rear end. If this is just a street car then I would probably go with the Eaton Posi or Yukon Dura Grip. There is a new differential out now that I have no experience with, but it looks good. It's the Power Trax Grip LS. That might be a good choice if your money it too tight for one of the others. The '87 will have the smaller 26 spline axles.
If you could find a good '90 to '92 rear end with a gear ratio that you like then that would be a better place to start. You would have the larger 28 spline axles and you wouldn't have to go through the set up process of installing another set of gears. You could install one of the differentials that I listed and be ready to go.
If you could find a good '90 to '92 rear end with a gear ratio that you like then that would be a better place to start. You would have the larger 28 spline axles and you wouldn't have to go through the set up process of installing another set of gears. You could install one of the differentials that I listed and be ready to go.
01-12-2015, 12:05 PM
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Re: RearEnd Upgrade
There are many ways to go with the 7.5 rear end. If this is just a street car then I would probably go with the Eaton Posi or Yukon Dura Grip. There is a new differential out now that I have no experience with, but it looks good. It's the Power Trax Grip LS. That might be a good choice if your money it too tight for one of the others. The '87 will have the smaller 26 spline axles.
If you could find a good '90 to '92 rear end with a gear ratio that you like then that would be a better place to start. You would have the larger 28 spline axles and you wouldn't have to go through the set up process of installing another set of gears. You could install one of the differentials that I listed and be ready to go.
If you could find a good '90 to '92 rear end with a gear ratio that you like then that would be a better place to start. You would have the larger 28 spline axles and you wouldn't have to go through the set up process of installing another set of gears. You could install one of the differentials that I listed and be ready to go.
awesome, that sounds good man
01-12-2015, 12:48 PM
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Re: RearEnd Upgrade
If you decide to go with the later rear end and just install a new differential this. http://www.nastyz28.com/forum/showthread.php?t=19773
01-12-2015, 09:04 PM
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Car: 1989 Iroc-Z Camaro
Engine: TBI,5.0
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Re: RearEnd Upgrade
If you don't have the money and don't want to save or just don't want to put this kind of cash into a 10 bolt then this would not be what you're looking for. A total rebuild =
This is a breakdown of my build. Some of these parts are necessary for the build and some can be changed to match your personal preference as in brand and style L.S.D./Locker.,etc.
Mine is a DD/have some fun car !
- 3.42 ring and pinion =$ 200.00
- master bearing kit = $ 90.0
- axle bearings and seals = $ 30.00
- 28 spline Eaton Posi. Unit = $ 500.00
- 28 spline axles = $250.00
- installation/labor = $ 300.00
- and if you want ,a LPW Ultimate support cover = $ 160.00 ( a little protection of the investment )
- That's $1,530.00 counting the cover.
- 3 year warranty on parts and labor
I'm not trying to discourage you from this but $$$.
Here's a link to the build if you want to see it. =
https://www.thirdgen.org/forums/transmissions-drivetrain/526958-10-bolt-upgrade-photos.html
Last edited by Ron U.S.M.C.; 01-12-2015 at 09:25 PM.
01-13-2015, 09:55 AM
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Re: RearEnd Upgrade
Good write up. I built mine on a "tight budget" with a used torsen & ring & pinion, and I was still into in a grand including the disc brake swap, but it was money well spent.
01-14-2015, 04:52 PM
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Re: RearEnd Upgrade
I agree.
If you're not racing it at the track but still want a decent gear ratio and posi unit like I did its worth it to me.
A two wheel peel just by just hitting WOT
from a stop ,hooking and barking the tires hitting second and again third shift in an auto. (bark),puts a smile on my face every time. ( street tires,Corvette Servo,3.42 and Eaton Posi )
Also a second to first drop down by letting off the throttle and then punching to WOT will again bark them from first to second and second to third .
All in my little 5.0 . That's just fun...........
If you're not racing it at the track but still want a decent gear ratio and posi unit like I did its worth it to me.
A two wheel peel just by just hitting WOT
from a stop ,hooking and barking the tires hitting second and again third shift in an auto. (bark),puts a smile on my face every time. ( street tires,Corvette Servo,3.42 and Eaton Posi )
Also a second to first drop down by letting off the throttle and then punching to WOT will again bark them from first to second and second to third .
All in my little 5.0 . That's just fun...........
Last edited by Ron U.S.M.C.; 01-15-2015 at 05:51 PM.
01-15-2015, 04:20 PM
#18
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Re: RearEnd Upgrade
Thanks for that @biggearhead @ron i was actually looking at your build the other day, ideally this would be perfect. Now just weighting the options, i appreciate the responses fellas
01-15-2015, 10:17 PM
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Re: RearEnd Upgrade
Depending where you are located, I'll have mine for sale soon. It's out of a 99 Z-28. Rebuilt about 13k miles ago. Aftermarket carrier ( Sorry not sure of the brand. Was in the car when I bought it. Richmond 4:10's. It will be complete drum to drum. Also have an aluminum driveshaft too.
01-17-2015, 01:04 PM
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Re: RearEnd Upgrade
Depending where you are located, I'll have mine for sale soon. It's out of a 99 Z-28. Rebuilt about 13k miles ago. Aftermarket carrier ( Sorry not sure of the brand. Was in the car when I bought it. Richmond 4:10's. It will be complete drum to drum. Also have an aluminum driveshaft too.
01-17-2015, 01:37 PM
#21
Re: RearEnd Upgrade
As someone else suggested... ride it til it breaks...
You could pick up an aluminum 10 bolt cover which will add some strength to it and can use it down the road...
I picked up a 91 rear end off craigslist for $60...
Took it apart, cleaned it, had it welded, powdercoated (all for cheap) and built it up with Eaton TrueTrac, Richmond 3.42 gears, Solid Spacer and Motive 28 Spline axles, LPW cover and Brace Kit, Yukon supreme mega giga warp drive rebuild kit.... It looks nice.. than had it switched out for the one in my car... gave it to my neighbor, now his car is getting faster (he had 2.73 gears, gonna have to sneak over and put bags of cement in his trunk
Not putting slicks on it... ever... should live a long time...
You could pick up an aluminum 10 bolt cover which will add some strength to it and can use it down the road...
I picked up a 91 rear end off craigslist for $60...
Took it apart, cleaned it, had it welded, powdercoated (all for cheap) and built it up with Eaton TrueTrac, Richmond 3.42 gears, Solid Spacer and Motive 28 Spline axles, LPW cover and Brace Kit, Yukon supreme mega giga warp drive rebuild kit.... It looks nice.. than had it switched out for the one in my car... gave it to my neighbor, now his car is getting faster (he had 2.73 gears, gonna have to sneak over and put bags of cement in his trunk
Not putting slicks on it... ever... should live a long time...
01-17-2015, 04:14 PM
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Re: RearEnd Upgrade
that looks reaaaalllyyy nice, i have been doing research over the past week or so on the subject, I am trying to do something similar to the process you took (used, rebuild, swap)
01-17-2015, 09:02 PM
#23
Re: RearEnd Upgrade
I was hustlin, as noted a 91 rear end, $60...
I got a smokin deal with coupons for Factory 10 28 spline axles from Advance (for 1,) but Jegs matched the price so I got 2... New Richmond gear off Ebay for $100 or less... I bought a "new TrueTrac" for a 10 bolt off ebay, $250, and later realized it was for a Ford 9", sold on ebay for $350 (made $100) and Summit / Eaton were having a $50 rebate, got the one I needed for $350 from Summit, normally $400.... I got the welding / powder coating done for $150, etc... again, ok for daily driver with street tires, but don't plan to put slicks on it...
I got a smokin deal with coupons for Factory 10 28 spline axles from Advance (for 1,) but Jegs matched the price so I got 2... New Richmond gear off Ebay for $100 or less... I bought a "new TrueTrac" for a 10 bolt off ebay, $250, and later realized it was for a Ford 9", sold on ebay for $350 (made $100) and Summit / Eaton were having a $50 rebate, got the one I needed for $350 from Summit, normally $400.... I got the welding / powder coating done for $150, etc... again, ok for daily driver with street tires, but don't plan to put slicks on it...
01-18-2015, 12:09 PM
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Re: RearEnd Upgrade
I was hustlin, as noted a 91 rear end, $60...
I got a smokin deal with coupons for Factory 10 28 spline axles from Advance (for 1,) but Jegs matched the price so I got 2... New Richmond gear off Ebay for $100 or less... I bought a "new TrueTrac" for a 10 bolt off ebay, $250, and later realized it was for a Ford 9", sold on ebay for $350 (made $100) and Summit / Eaton were having a $50 rebate, got the one I needed for $350 from Summit, normally $400.... I got the welding / powder coating done for $150, etc... again, ok for daily driver with street tires, but don't plan to put slicks on it...
I got a smokin deal with coupons for Factory 10 28 spline axles from Advance (for 1,) but Jegs matched the price so I got 2... New Richmond gear off Ebay for $100 or less... I bought a "new TrueTrac" for a 10 bolt off ebay, $250, and later realized it was for a Ford 9", sold on ebay for $350 (made $100) and Summit / Eaton were having a $50 rebate, got the one I needed for $350 from Summit, normally $400.... I got the welding / powder coating done for $150, etc... again, ok for daily driver with street tires, but don't plan to put slicks on it...
yeaaa I have no intentions of putting slicks on this one, I have a fully built 85MCSS with draglights,12.5 sportsman pros and 4.11 minispool rearend for serious racing. Just want a little more pep in the Trans for those "stoplight to stoplight" situations 
01-18-2015, 07:58 PM
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Re: RearEnd Upgrade
The 3.08 first gear in the 700r4 auto came factory with a 3.23:1 as the performance gear. You might be OK stepping up to 3.42, but 3.73 with the auto is usually considered to low of a rear gear.
01-18-2015, 11:27 PM
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Re: RearEnd Upgrade
If your OK with your gear ratio this could work =
http://www.powertrax.com/index.php/p...ertrax-no-slip
http://www.powertrax.com/index.php/p...ertrax-no-slip
01-19-2015, 01:51 AM
#31
Re: RearEnd Upgrade
If your OK with your gear ratio this could work =
http://www.powertrax.com/index.php/p...ertrax-no-slip
http://www.powertrax.com/index.php/p...ertrax-no-slip
01-19-2015, 10:21 AM
#32
Re: RearEnd Upgrade
With 350 TPI, I would go 3.23 or 3.42... the 3.73, neeeds good traction and others say it changes the power band of where the TPI is happiest...
As for differential...
The clutch style ones...
Good straight line...
But give power to wheel with less traction when turning or slipping...
The gear ones.... True Trac, like I got...
Good straight line...
Give power to the wheel with traction...
Not sure about the powermax one above...
As for differential...
The clutch style ones...
Good straight line...
But give power to wheel with less traction when turning or slipping...
The gear ones.... True Trac, like I got...
Good straight line...
Give power to the wheel with traction...
Not sure about the powermax one above...
02-01-2015, 10:53 PM
#33
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Car: 87
Engine: TPI L98
Transmission: 700r4
Axle/Gears: stock
02-01-2015, 10:57 PM
#34
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Car: 87
Engine: TPI L98
Transmission: 700r4
Axle/Gears: stock
Re: RearEnd Upgrade
Alright, thanks. Did all 700r4s come with that 3.08? If so then I'm fine with 3.23s compared to spending them cash on 342, I'm just not sure what it has currently.
02-01-2015, 11:00 PM
#35
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Car: 87
Engine: TPI L98
Transmission: 700r4
Axle/Gears: stock
Re: RearEnd Upgrade
If your OK with your gear ratio this could work =
http://www.powertrax.com/index.php/p...ertrax-no-slip
http://www.powertrax.com/index.php/p...ertrax-no-slip
02-01-2015, 11:01 PM
#36
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Car: 87
Engine: TPI L98
Transmission: 700r4
Axle/Gears: stock
02-01-2015, 11:03 PM
#37
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Car: 87
Engine: TPI L98
Transmission: 700r4
Axle/Gears: stock
Re: RearEnd Upgrade
With 350 TPI, I would go 3.23 or 3.42... the 3.73, neeeds good traction and others say it changes the power band of where the TPI is happiest...
As for differential...
The clutch style ones...
Good straight line...
But give power to wheel with less traction when turning or slipping...
The gear ones.... True Trac, like I got...
Good straight line...
Give power to the wheel with traction...
Not sure about the powermax one above...
As for differential...
The clutch style ones...
Good straight line...
But give power to wheel with less traction when turning or slipping...
The gear ones.... True Trac, like I got...
Good straight line...
Give power to the wheel with traction...
Not sure about the powermax one above...
02-01-2015, 11:45 PM
#38
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Car: 1989 Iroc-Z Camaro
Engine: TBI,5.0
Transmission: Automatic 700R4
Axle/Gears: Eaton Posi,3.42,LPW Ultimate Cover
Re: RearEnd Upgrade
I would pick the gear that has been suggested most often with a TPI/700r4. = 3.42
so if you have the opportunity to get them than I would.
so if you have the opportunity to get them than I would.
Last edited by Ron U.S.M.C.; 02-02-2015 at 01:04 AM.
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